That's slightly fewer new infections than the CDC's last estimate of 56,300 for 2006. But that's due to improvement in the way CDC calculates new HIV infections, not to a drop in the spread of HIV in the U.S.

Infection rates were stable from 2006 to 2009, the latest year included in CDC figures.

"Not increasing is not good enough. The number of new HIV infections remains far too high," CDC Director Thomas Frieden, MD, said at a news teleconference held to announce the new numbers.

As of 2009, 61% of new HIV infections are in men who have sex with men. New infections from heterosexual contact make up 27% of the total, while new infections among users of intravenous drugs represent only 9%.

Here's why the HIV infection rate isn't going down: There's been a sharp increase in new infections among gay and bisexual men. From 2006 to 2009, new infections among young men who have sex with men are up 34%.

Even more striking is the 48% increase in new HIV infections among black gay and bisexual men ages 13 to 29.

"We are very concerned about that trend," Frieden said.

Why such a high rate among these young black men? Frieden noted that black gay/bi men do not have more individual risk factors than white gay/bi men.

"These black men have fewer sex partners, are less likely to use drugs when having sex, and are no more likely to report unprotected anal intercourse than white men," Frieden said. "We think it is other factors. Young black men have more sexually transmitted infections. Black men who have sex with men are also more likely to have undiagnosed infections. And there are other factors, such as limited access to health care and the stigma of homosexuality."

Most people who come down with HIV are infected by someone who doesn't know he or she is carrying the AIDS virus. The CDC estimates that 21% of people living with HIV don't know they're infected.

CDC to Target Proven Prevention Efforts

That's why universal HIV testing is the cornerstone of the CDC's HIV prevention program. But Frieden was quick to note that testing is only part of the solution.

"What we have come to understand is the linkage between treatment and prevention," he said. "But it is not enough to promote testing and linkage to care. We have to promote treatment and continuity of care. We have to make sure people with HIV live long, healthy lives and that we reduce the risk of those around them as well."

"We work with HRSA [the U.S. Health Resources and Services Administration] and others to reduce the cost of HIV medications, which we think has significant potential for prevention," Frieden said. "And it is important that each state recognize it has the responsibility to take care of the people with HIV within their state -- and to prevent new infections."

Kevin Fenton, MD, PhD, director of the CDC's AIDS center, said at the teleconference that the CDC is targeting young gay men -- young black men in particular -- with HIV prevention efforts.

"This would mean putting extra resources into the communities most impacted by HIV," Fenton said. "For example, we now require all jurisdictions we fund to do a limited number of high-impact interventions: condom promotion scale-up, increased testing, better partner services -- in other words, directing grantees to focus on high-impact activities."